Tonight, pregnant at 61. When her young daughter needed a surrogate, one woman stepped up, giving birth and becoming a grandmother at the same time. And she is not alone. In fact, an illinois woman gave birth to her granddaughter just last week. But to quote president lyndon johnson, our problem is not making miracles. It's managing them. Just because a woman can do this, doesn't mean that she should. Here's abc's amy robach with one family's story. Reporter: Little finn and his grandmother share a very rare bond. Not only is she his grandmother, but she's also his surrogate mother. How could that possibly happen? No offense, but who would do that? And what doctor would let them do that? We kept thinking, we were going to be stopped anywhere along the way. At every turhey kept saying, well you're really in amazing shape. Reporter: Chris gave birth to her grandson as the surrogate for our daughter sarah and son-in-law's fertilized egg. We thought we'd ask a doctor about this and they would say, it's time to move on. Or call the psych ward. Reporter: It wasn't the way sarah and bill imagined having a baby and it was a long hard fought road that led them down this path. Sarah and a professional life coach who had a major life issue of her own. There was nothing I could do with myself to make my body do this, become pregnant the way we wanted. Reporter: You tried everything? We did. Reporter: They tried many treatments and a total of six rounds of in vitro fertilization. There's financial depletion, emotionally. They did get pregnant through ivf, and were going to have twins, but at 22 weeks, something went wrong. I woke up, felt completely fine, suddenly had a cramp, and I just saw blood. Everything in me was, please be a dream. She miscarried the dreams and tried ivf two more times, resulting in another pregnancy, but just six weeks later, another miscarriage. That's when I really started to question, would we ever even be able to have children? Reporter: Meanwhile newly retired chris was searching for her next calling when the inspiration came to her. It just hit like a ton of bricks. Reporter: Did you feel crazy for even thinking it? Oh, yeah. Reporter: Then you had to probably feel crazier saying it out loud. I had to go to my husband first. Reporter: I want to know what your reaction was. I was stunned. Absolutely stunned. The hardest thing in contemplating pursuing this idea, first and foremost, what are the risks to my mother's health? Reporter: So they consulted with a doctor, who had conducted sarah's repeated ivf treatments. Reporter: Is a 60-year-old woman a good candidate for surrogacy? No. In general, the answer is no. But some 60-year-olds perfectly capable of carrying a pregnancy. Reporter: Chris received the traditional hormone treatments that prepare her uterus with pregnancy. It took two attempts, 30 years after her last pregnancy. Reporter: Were you ever embarrassed being pregnant and 60? I really was. Especially at the beginning. I thought, I tried to go in and buy some new pants on my own. So I of course said, I have a daughter about my size, and she's expecting a baby. I trusted her body. Even though anyone could say to me, that's insane, she's advanced age wise, it's never been done. But I trusted her body. Was it difficult at all seeing your mother-in-law carrying your child? How did your head deal with that? If you go through the things that we went through, it changes your perception of reality. Reporter: The closely monitored pregnant ran its course without any complications and in due time. Nine months pregnant, 38 and a half weeks. Amazing. Reporter: At the age of 61. Mama, how are you doing? Grand mama? Reporter: Finn finally arrived. What did the delivery look like? The whole room was just holding their breath. Until that moment, I had complete confidence and then i was just like, oh, god, breathe. Just got to breathe. And I did. It was the opposite of the heart breaking. It was like a cracking and it was amazing. Yeah. Want to go see the fire truck? Reporter: Like ivf was 35 years ago, advances in surrogacy today is a game-changer. A pregnancy at 61 is still unusual, but for them, it's a medical miracle. This is just how he got here. We absolutely see this in our family as something to celebrate. Reporter: Grandma chris says she doesn't plan on carrying another child, but sarah is optimistic that perhaps someday she'll be pregnant again. Yeah! Reporter: For "nightline," I'm amy robach in chicago. Sarah's book is in stores now.

This transcript has been automatically generated and may not be 100% accurate.

Surrogate Mother Gives Birth to Her Grandson

null

{"id":17187913,"title":"Surrogate, 61, Gave Birth to Grandson","duration":"3:00","description":"Woman carried and gave birth to her daughter's child when she couldn't carry a baby to term.","section":"Nightline","mediaType":"Default"}